A thin film type field-effect transistor (FET) is a basic structure in a microelectronic field. The FET includes three electrodes, that is, a source electrode, a drain electrode, and a gate electrode, an insulating layer, and a semiconductor layer. In the case of when the above semiconductor layer is a conductive channel between the two above electrodes, that is, the source electrode and the drain electrode, the FET acts as a capacitor. In the above channel, the concentration of the charge carrier is controlled by using voltage that is applied through the gate electrode. As a result, a flow of electric charges between the source electrode and the drain electrode may be controlled by voltage that is applied through the above gate electrode.
Recently, a concern has been grown rapidly about FETs using an organic semiconductor material. In the case of when the organic semiconductor material is used, electronic devices may be produced by using a printing process such as screen-printing, ink-jet printing, or micro-contact printing. In addition, in the case of when the above material is used, the process may be performed at a very low temperature of the substrate in a state where a vacuum is not required as compared to the case of when a known inorganic semiconductor material is used. Therefore, the electronic device using the organic semiconductor material including FETs may be produced under a very soft production condition at the low cost as compared to the case of when the inorganic semiconductor material is used.
Studies have been conducted to use organic materials such as small molecules, polymers, and oligomers as an organic semiconductor material in FETs since the 1980s. With respect to results of studies in the above-mentioned field, in views of the charge carrier mobility in FETs, performance of the organic FET is increased from 10−5 cm2/Vs to 1 cm2/Vs (J. M. Shaw, P. F. Seidler, IBM J. Res. & Dev., Vol. 45, 3 (2001)). The performance of the organic transistor is as good as that of a current amorphous silicon transistor. Thus, the organic transistor may be applied to E-papers, smart cards, or display devices.
In order to improve the performance of the organic FET, efforts have been made to mix conductive particles and semiconductor organics with each other. Scientists of AIST in Japan announced test results that when P3HT and Ag nanoparticles were mixed with each other to form a semiconductor layer, an off current was reduced, in other words, the Ag nanoparticles acted as an antioxidant. However, in the above results, since the conductive particles are not present in the conductive channel but between alkyl groups of P3HT, the charge mobility cannot be improved.